Meaning: 'Landscape' refers to the visible features of an area of land, including its physical geography and scenery.

Wrong options:

• security: The term 'security' refers to safety or protection, which does not relate to the physical characteristics of a location in the context of ecotourism.
• symptom: 'Symptom' denotes a sign of a condition or disease, which is irrelevant in this context as it does not pertain to physical characteristics of a place.
• plant: While 'plant' refers to flora, it is too specific and does not encompass the broader physical features of an area like 'landscape' does.

Correct answer: sustainable

Explanation: The term 'sustainable' is an adjective that describes travel that meets present needs without compromising future generations, fitting perfectly in the context of ecotourism. It aligns with the environmental movement's goals and maintains grammatical structure as it modifies 'travel'.

Meaning: 'Sustainable' means capable of being maintained over the long term without harming the environment, which is a core principle of ecotourism.

Wrong options:

• acquired: 'Acquired' suggests something obtained, which does not relate to the concept of travel that is environmentally friendly or responsible.
• obtainable: Similar to 'acquired', 'obtainable' implies something that can be gotten, lacking the environmental connotation necessary for this context.
• preventable: 'Preventable' refers to something that can be avoided, which does not fit the context of describing a type of travel.

Correct answer: prevalent

Explanation: The word 'prevalent' is an adjective that means widespread or commonly occurring, which fits the context of ecotourism becoming a recognized travel concept. It aligns grammatically as it describes the state of ecotourism in the late 1980s.

Meaning: 'Prevalent' means existing or happening frequently, indicating that ecotourism became a popular choice among travelers.

Wrong options:

• opulent: 'Opulent' describes something luxurious or wealthy, which does not relate to the concept of ecotourism as it focuses on low-impact travel.
• ambivalent: 'Ambivalent' means having mixed feelings, which does not apply to the context of ecotourism's acceptance as a travel concept.
• equivalent: 'Equivalent' refers to something equal in value or meaning, which does not fit the context of describing the popularity of ecotourism.

Correct answer: specializing

Explanation: The term 'specializing' is a verb that indicates a focus on a particular area, which fits the context of organizations that concentrate on ecotourism. It maintains grammatical consistency as it describes the actions of these organizations.

Meaning: 'Specializing' means to focus on a specific area of expertise or activity, indicating that these organizations are dedicated to ecotourism.

Wrong options:

• trivializing: 'Trivializing' means making something seem less important, which contradicts the positive focus on ecotourism.
• conceptualizing: 'Conceptualizing' refers to forming a concept or idea, which does not fit the context of organizations actively engaging in ecotourism.
• orientalizing: 'Orientalizing' refers to depicting or representing Eastern cultures in a stereotypical way, which is irrelevant to the context of ecotourism.